This application relates to and claims priority to corresponding Japanese Application No. 2001-344429, which was filed on Nov. 9, 2001, and corresponding Japanese Application No. 2002-246060, which was filed on Aug. 27, 2002.
This application relates to and claims priorities from corresponding Japanese Patent Application No. 2001-344429 filed on Nov. 9, 2001 and Japanese Patent Application No. 2002-246060 filed on Aug. 27, 2002.
1. Field of the Invention
The present invention relates to a color sorting apparatus for sorting out colored granular objects or foreign objects which have been mixed into the raw granular objects such as grains or resin pellets, and more particularly to an optical detection device for use in such color sorting apparatus.
2. Description of the Related Art
A conventional known color sorting apparatus of this kind is so constructed that raw granular objects supplied from an upper portion of an inclined flow chute flow down on the flow chute; light is irradiated on the granular objects which are released from a lower end of the flow chute along a falling locus A; light obtained from each granular object arriving and passing at an optical detection position is detected by an optical sensor; and the colored granular objects or foreign objects are determined based on the detected signal and removed from the remaining acceptable granular objects. As the above optical sensor, used is a CCD linear sensor which utilizes the three primary colors of RGB (Red, Green and Blue) for the detection of the colored granular objects (hereinafter referred to as a xe2x80x9ccolor CCD linear sensorxe2x80x9d).
The color CCD linear sensor includes the following types. As a first type, as shown in FIG. 10, a CCD linear sensor 100 having a filter which allows only the red (R) wavelength to pass (hereinafter referred to as xe2x80x9cR-CCD linear sensorxe2x80x9d), a CCD linear sensor 101 having a filter which allows only the green (G) wavelength to pass (hereinafter referred to as xe2x80x9cG-CCD linear sensorxe2x80x9d) and a CCD linear sensor 102 having a filter which allows only the blue (B) wavelength to pass (B-CCD linear sensor) are independently arranged. In FIG. 11, there is shown a modified arrangement in which a dichroic mirror 103 is provided to cause the reflected and transmitted light to enter the respective R-, G- and B-CCD linear sensors 100, 101 and 102.
As a second type, as shown in FIG. 12, there is another arrangement in which the R-CCD linear sensor 100, the G-CCD linear sensor 101 and the B-CCD linear sensor 102 are arranged vertically in three rows.
As a third type, as shown in FIG. 13, there is an in-line type CCD linear sensor 104 in which a light receiving element 104a with a filter permitting the passing of only the red (R) wavelength, a light receiving element 104b with a filter permitting the passing of only the green (G) wavelength and a light receiving element 104c with a filter permitting the passing of only the blue (B) wavelength are sequentially arranged in one row.
However, the above explained conventional CCD linear sensors have the following problems. As for the first type, since three separate CCD linear sensors 100, 101 and 102, and the dichroic mirror 103 are necessitated, the dimension and the cost of the optical detection device unavoidably become large and high. As for the second type, the dimension of the device can be more compact than that of the first type because the three CCD linear sensors 100, 101 and 102 are integrally arranged in three rows. However, to the respective R-CCD linear sensor 100, G-CCD linear sensor 101 and B-CCD linear sensor 102, light from the focal points X1, X2 and X3 which are not on the same optical detection point X but are deviated vertically with one another enters as shown in FIG. 12. For this reason, with respect to the surface of the granular object which is subjected to the optical detection, the optical detection for the respective RGB wavelengths within one scanning is performed based on the individual focal points X1, X2 and X3. For example, from the point where R-wavelength is detected, no detection of G- and B-wavelength data is performed. That is, it has been difficult to obtain the RGB-wavelength data from the entire surface of the object to be optically detected. Therefore, there has been a demand of further improvement in the precision of acceptable and unacceptable detection based on RGB-wavelength data.
As for the third type, since this is a horizontally in-line CCD linear sensor 104, the dimension of the optical detection device can be made more compact than that of the second type. However, since the structure of the CCD linear sensor 104 is such that, as described above, the filter which allows the passing of only the R-wavelength, the filter which allows the passing of only the G-wavelength and the filter which allows the passing of only the B-wavelength are sequentially arranged in one row, the respective R-, G- and B-wavelengths are optically detected from one side to the other side at the optical detection position X as shown in FIG. 14. For this reason, with respect to the optically detected surface of one granular object S, for example, the G- and B-wavelengths are not optically detected at the portion where the R-wavelength has been detected as understood from FIG. 15. Therefore, there has been a demand of further improvement in the detection accuracy on the RGB basis in the same manner as in the above second type.
Therefore, the principal object of this invention is to provide an optical sorting apparatus for granular objects in which the sorting accuracy is enhanced and the cost thereof is reduced.
According to the present invention, there is provided a color sorting apparatus for granular objects comprising:
a transferring means for transferring raw granular objects to an optical detection area;
an optical detection means arranged around a falling locus of the raw granular objects which are released from the transferring means, the optical detection means comprising a CCD linear sensor, an illuminating means and a background means, the optical detection means functioning to detect light from the background means and each of the granular objects irradiated by the illuminating means, the CCD linear sensor including a plurality of light receiving elements arranged in at least one row, each being capable of detecting red, green and blue wavelengths, and the illuminating means including a red light source, a green light source and a blue light source;
a control means for determining whether a granular object at the optical detection area is an acceptable one or an unacceptable one based on the comparison between the detected light signal received by the CCD linear sensor and a threshold value established in advance, wherein the control means sequentially switches over the red, green and blue light sources while the granular object is passing within the optical detection area, and wherein the CCD linear sensor receives light from the granular object in synchronization with the switching of said light sources; and
a sorting means for removing the unacceptable granular object from the falling locus in response to a rejection signal from the control means.
In the above color sorting apparatus, it is preferable that a condition Vxe2x89xa6L/3T is satisfied, wherein T represents a speed of one scanning of the CCD linear sensor, V represents a falling speed of the granular object, and L represents a length of the optical detection area for the CCD linear sensor in the direction of the falling locus.
According to the above arrangement, the red, green and blue light sources are sequentially switched over while the granular object is passing within the predetermined optical detection area and, in synchronization with this switching operation of the light sources, the CCD linear sensor detects the red, green, blue wavelengths from the entire surface of each granular object to be optically detected. In this way, it is possible to obtain a color signal consisting of three, red, green and blue wavelengths from the entire surface of the granular object to be optically detected.